1. Technical Field
The present invention relates generally to semiconductor fabrication, and more particularly, to forming a capping layer over a metal wire structure in a partially fabricated semiconductor device using selective atomic layer deposition.
2. Related Art
Metal migration is the diffusion of molecules of a metal conductor (such as copper or aluminum) into surrounding dielectric such as silicon dioxide or polymers from exposure to high temperatures, which ultimately leads to current leakage and device failure. Electromigration is the movement of atoms of a metal conductor in response to the passage of high current through it, which can lead to the formation of “voids” in the conductor that can grow to a size where the conductor is unable to pass current. Typically, metal migration and electromigration have been addressed by providing liners about metal conductors; these liners hinder or forestall these effects.
One challenge with providing liners is generating a liner or capping layer on the upper surface of a metal wire structure. In particular, metal wires are typically formed by a Damascene process in which a metal wire's pattern is first lithographically defined in a layer of dielectric, and then a metal is deposited to fill resulting trenches. Excess metal is then removed by means of chemical-mechanical polishing (planarization), which leaves an upper surface of the metal exposed, i.e., with no capping layer and no means of preventing metal migration or electromigration. One approach to generating a capping layer on a copper line is disclosed in U.S. Pat. No. 6,844,258 to Fair et al. In this approach, a refractory metal nucleation layer is deposited and then at least the upper portion of the refractory metal layer is nitrided to form a refractory metal nitride. One shortcoming of this approach, however, is that it is fairly complicated.
In view of the foregoing, there is a need in the art for methods of forming a capping layer over a metal wire structure that do not suffer from the problems of the related art.